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The nature of the lithosphere beneath the Sardinian continental block: Mantle and deep crustal inclusions in mafic alkaline lavas

Ruffer, Michael J. (1987) The nature of the lithosphere beneath the Sardinian continental block: Mantle and deep crustal inclusions in mafic alkaline lavas. Lithos, 20 (3). pp. 225-234. ISSN 0024-4937. https://resolver.caltech.edu/CaltechAUTHORS:20190214-150247316

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Abstract

Ultramafic and mafic rocks are abundant as inclusions in Plio-Pleistocene alkali basalt, trachybasalt and basanite magmas. They provide an important “window” into the nature of the lithosphere beneath the Sardinian continental block. The inclusions are predominantly porphyroclastic-textured spinel peridotites, although pyroxenites, mafic granulite-facies gneisses and augite megacrysts also occur. Equilibration temperatures of 956 ± 34°C, using the Wells geothermometer, imply that the peridotites were entrained by rising alkalic magmas somewhere near the top of the mantle lithosphere. Pyroxenites and augite megacrysts are more Fe-rich and have lower CrAl ratios than clinopyroxenes from peridotite, and may have precipitated from mafic magmas at mantle pressures. The available evidence strongly implies considerable chemical and mineralogical heterogeneity in the upper mantle lithosphere beneath Sardinia. Diopside mineral separates from two spinel peridotite xenoliths are characterised by (LaYb)_N > 1 and a chondrite-normalised U-shaped REE pattern, which cannot be explained by a single stage partial melting event. Trace element constraints imply that the rare samples of the deep crust, now granulite-facies gneisses, were originally gabbroic cumulates.


Item Type:Article
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https://doi.org/10.1016/0024-4937(87)90010-7DOIArticle
Additional Information:© 1987 Published by Elsevier B.V. Received 16 May 1986, Accepted 7 October 1986. This work was carried out while the author held a NERC research studentship at Imperial College, London. Dr. R.N. Thompson is thanked for his encouragement and advice. Paul Suddaby and Nick Royall are thanked for their help with the electron microprobe. Dr. J.N. Walsh made available ICP facilities at King's College, London. Analytical work at Imperial College depended much on the help and advice of Dr. J. Nolan and Peter Watkins. Instrumental neutron activation counting facilities were made available by Dr. T. Williams at the British Museum. Isotopic analyses were obtained at the University of Oxford, where thanks are due to Drs. S. Moorbath (through an NERC research grant) and P. Taylor and to Roy Goodwin. Constructive criticism by A. Dana Johnston and an anonymous reviewer are much appreciated.
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Funding AgencyGrant Number
Imperial College LondonUNSPECIFIED
Natural Environment Research Council (NERC)UNSPECIFIED
Issue or Number:3
Record Number:CaltechAUTHORS:20190214-150247316
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190214-150247316
Official Citation:Michael J. Rutter, The nature of the lithosphere beneath the Sardinian continental block: Mantle and deep crustal inclusions in mafic alkaline lavas, Lithos, Volume 20, Issue 3, 1987, Pages 225-234, ISSN 0024-4937, https://doi.org/10.1016/0024-4937(87)90010-7. (http://www.sciencedirect.com/science/article/pii/0024493787900107)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92948
Collection:CaltechAUTHORS
Deposited By: Gail Peretsman Clement
Deposited On:19 Feb 2019 22:50
Last Modified:03 Oct 2019 20:50

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